1. Field of the Invention
The present invention relates to a method for measuring a radio-frequency current outputted from a radio-frequency power supply, and more particularly to a method for easily measuring a radio-frequency current.
2. Description of the Related Art
FIG. 10 is a schematic view showing a constitution of a plasma etching apparatus 90. The plasma etching apparatus is a dry-etching apparatus utilizing plasma of reactive gas generated by radio-frequency discharge. As shown in FIG. 10, a radio-frequency output from a radio-frequency (RF) power supply 1 is supplied to a main unit 3 through a matching box 2. The main unit 3 has a cathode electrode 3a electrically connected to the matching box 2 and an anode electrode 3b connected to a ground potential in a reaction chamber 31 which is a vacuum container. In etching, the plasma of the reactive gas is generated by the radio-frequency discharge between the cathode electrode 3a and the anode electrode 3b.
The radio-frequency power supply 1 and the matching box 2 are electrically connected with a coaxial cable 4 while the matching box 2 and the main unit 3 are electrically connected with a coaxial cable 5.
Next, operation of the plasma etching apparatus will be discussed. For example, the radio-frequency output from the radio-frequency power supply 1 is supplied between the cathode electrode 3a and the anode electrode 3b through the coaxial cable 4, the matching box 2, and the coaxial cable 5 as a traveling wave, to generate the plasma of the reactive gas between the cathode electrode 3a and the anode electrode 3b. The radio-frequency output supplied as a traveling wave is consumed to maintain the plasma of the reactive gas. At this time, some of the traveling wave is reflected by the plasma of the reactive gas and goes back to the matching box 2 through the coaxial cable 5 as a reflected wave. The matching box 2 performs matching using a combination of a coil (L) and a capacitor (C) to counteract the reflected wave, and therefore almost all the traveling wave is supplied to a load.
The radio-frequency power supply 1 is provided with an output meter to monitor the radio-frequency output, and when the reflected wave increases due to some abnormality, the output meter does not indicate a predetermined radio-frequency output, to thereby indicate occurrence of an abnormality.
In this case, a radio-frequency power-meter sensor 10a is interposed between the matching box 2 and the main unit 3, as shown in FIG. 11. The radio-frequency power-meter sensor 10a has an input terminal connected to the coaxial cable 5 disconnected from the main unit 3 and an output terminal connected to the main unit 3 with a coaxial cable 10b. This is referred to as "an in-line mode". Further, the radio-frequency power-meter sensor 10a is connected to a radio-frequency power meter 10 to measure the radio-frequency output from the radio-frequency power supply 1. The radio-frequency power-meter sensor 10a is a directional coupler, and the radio-frequency power meter 10 has a constitution to simultaneously indicate the traveling wave and the reflected wave.
When the abnormality occurs, since the value of the traveling wave decreases and the value of the reflected wave increases, a parameter for generating the plasma should be controlled to decrease the value of the reflected wave and the connection of the coaxial cables should be checked.
Thus, in an apparatus using the radio-frequency power supply such as the plasma etching apparatus, the radio-frequency power-meter sensor 10a is interposed between the matching box 2 and the main unit 3 to measure the radio-frequency current when some abnormality occurs. Therefore, there arises the necessity for disconnecting the coaxial cable 5 from the main unit 3 and connecting it to the radio-frequency power-meter sensor 10a and for connecting the radio-frequency power-meter sensor 10a and the main unit 3 with the different coaxial cable 10b.
If the abnormality occurs due to poor connection at a connector of the coaxial cables, for example, the abnormality is resolved by changing the connecting condition at the connector through interposing the radio-frequency power-meter sensor 10a, and the cause of the abnormality is not clarified.
Furthermore, the voltage/current meter for the radio-frequency output built in the radio-frequency power supply or the radio-frequency power meter connected in the in-line mode can indicate only a total of the radio-frequency output and a costly measurement system is required in order to measure superimposition of spurious components such as higher-order harmonics or subtle variation of the radio-frequency output, and moreover, obtained are data after advanced-processing with a computer such as noise cuts, not original radio-frequency output.